1. Field of the Invention
The present invention relates to an ink-jet apparatus and a method of controlling an ink-jet head for use in the ink-jet apparatus, and more particularly to an ink-jet apparatus adopting an ink-jet head that uses thermal energy for ejecting liquid, and also a method of controlling the ink-jet head through estimation of the temperature thereof.
2. Description of the Related Art
An ink-jet method capable of applying extremely small quantity of liquid to a printing medium has been often used so far in various fields such as letter printing, image printing, textile printing and so on, and is now expected to be applied to other fields, so that it is admitted as a very practical technique.
For example, due to a recent diffusion of personal computers, word processors, facsimile apparatuses and so on to many offices and individual homes, various printers respectively adopting different recording methods have been developed as the output apparatuses for those machines. Among these output apparatuses, since a printing apparatus adopting an ink-jet printing method has various benefits such as its low noise, its capability of outputting a high-quality print on a printing medium of various types, and also its small size and so on, it is optimum for a personal use even in offices. Among those ink-jet printing methods, a thermal method such as bubble-jet method (which is proposed by CANON INC.) having rapid drivability in response to a request for its activation has now become the most widely diffused method. The printing apparatus adopting this method first converts electric signals to thermal energy by use of heating elements at the print head portion, and causes nucleate or film boiling with respect to the ink, and thereafter utilizes the pressure thus generated to eject the ink onto the printing medium.
An ink drop applied onto the printing medium is expanded to form a dot. An image is formed by a set of formed dots and it is thus printed on the printing medium. The area of each dot greatly depends on the size of the ink drop, namely, the ink-ejecting amount. Therefore, the most important factor for acquiring a high-quality print adopting the ink-jet printing method is to control the amount of ink ejection.
The amount of ink ejection is closely related with the temperature of ink or the ink-jet head, and increases in accordance with a rise of temperature. For this reason, the critical problem from the technical viewpoint for acquiring a high-quality print is to control the temperature of ink or ink-jet head
As one of the means for detecting the temperature of ink-jet head of the thermal method, providing a temperature sensor to the ink-jet head is widely adopted. However, for providing a temperature sensor, there exist some problems to be considered such as the rise of the total cost that may be caused by attaching a means for amplifying or modulating the electric signal corresponding to the thus detected temperature or a noise avoiding means, and an adverse effect which may possibly be caused by a temperature inclination derived from the distance between the position of the portion to be actually detected (such as a heating element on the head) and that of the temperature sensor.
In order to overcome these aforementioned problems, the assignee of this invention has disclosed a method of obtaining the temperature of the ink-jet head by a means for obtaining ambient temperature around the printing device or ink-jet head by using a sensor or the like, and also by a means for estimating a rise of temperature of the ink-jet head from the amount of heat applied to the ink-jet head within a predetermined period of time, as is disclosed in the Japanese Patent Application Laying-open No. 5-208505 and No. 7-125216.
On the other hand, as an ink-jet head adopting the thermal method, one that includes a plurality of ink ejecting heaters (hereinafter may be referred to just as ejection heaters) provided with respect to only one ejection orifice has been proposed. The ink-jet head of this type can control the amount of ink ejection in a step-by-step manner by changing the number of ejection heaters used for one ink ejecting operation. Moreover, in this type of ink-jet head, if a very detailed printing is required, a high-resolution image can be realized by forming ink dots made of relatively small ink-ejecting amount, whereas in a case in which a so-called "full-dot" or "solid" printing is required, the printing efficiency can be improved by forming the ink dots by making the ink ejecting amount relatively large.
However, in the aforementioned ink-jet heads to which a plurality of ink ejection heaters are provided, it has not yet been proposed that the temperature rise of an ink-jet head is estimated from the amount of heat applied thereto within a predetermined time of period in order to obtain the temperature thereof, and the temperature detecting method in the case of providing only one ejection heater with respect to only one ejection orifice can not be applied as it is.